Expanded low density polyphenylene ether resin compositions exhibit superior thermal properties compared to conventional expanded polystyrene. Expanded low density polyphenylene ether resin compositions of the present invention will provide better Continuous Use Temperature (C.U.T.) performance than conventional EPS materials. Furthermore, polyphenylene ethers provide a degree of inherent flame resistance not available from styrenic resins.
These low density polyphenylene ether resin compositions will provide better mechanical properties as the PPE content is increased. Such materials can be used in traditional EPS applications such as those requireing energy absorption (e.g. knee restraints), sound insulation, and heat insulation.
The polyphenylene ether resins (PPE) are known to be combinable with alkenyl aromatic polymers (PS) to provide thermoplastic compositions which are extrudable and moldable into articles of high heat resistance, good impact strength and hydrolytic stability, and good dimensional stability. The compositions can also be formulated into various types, including flame retardant, reinforced, platable, or foamable grades.
The polyphenylene ether resins and method of their formation are described in the patent literature, including U.S. Pat. Nos. 3,306,874 and 3,306,875 (Hay), and U.S. Pat. Nos. 3,257,357 and 3,257,358 (Stamatoff). A mixture of polyphenylene ether resin with poly(alkenyl aromatics), including polystyrene, rubber modified polystyrene and styrenic co-and terpolymers is disclosed by Cizek, in U.S. Pat. No. 3,383,435.
Several grades of foamable PPE/PS blends are available commercially. These typically will be used to fabricate structural foam parts utilizing molds and techniques analogous to injection molding processes. Additionally, these structural foam compositions are chemically foamed, and typically exhibit densities far greater than the expandable PPE/PS compositions of the present invention. Conventional PPE/PS structural foam exhibits densities in excess of 50 lbs./ft.sup.3. Such injection moldable foam materials are quite distinct from the low density PPE/PS compositions of the present invention which exhibit densities less than 20 lbs./ft.sup.3.
It has now been discovered that PPE and PPE/PS materials having densities less than 20 lbs./ft.sup.3 can be provided by the process of the present invention. Furthermore it is now possible to provide PPE based foams having densities less than 2 lbs./ft.sup.3.